This invention relates to fluid pumps. More specifically, this invention relates to a gear pump including a floating bushing arrangement enabling use of the gear pump for pumping a fuel with poor lubricating qualities at relatively high speeds and pressures.
Gear pumps in general are well known in the prior art, and typically comprise a matched set of meshing spur gears carried on parallel rotating shafts, and mounted in a generally figure-eight shaped chamber within a pump housing. The gears are rotated together to pump a fluid from a housing inlet port to an outlet port. Gear pumps of the prior art are most commonly used for pumping hydraulic fluids, such as oil, wherein inherent leakage within the housing is advantageously used to lubricate shaft bearings.
Gear pumps frequently are preferred over vane-type or reciprocating pumps because of their continuous flow capability, relatively accurate metering characteristics, and long term reliability. Moreover, gear pump output is relatively easily controlled by controlling the rotational speed of the pumping gears. However, the use of gear pumps has been limited in the prior art to relatively low speed and/or pressure pumping applications wherein the pumped fluid comprises a relatively viscous fluid, such as oil, satisfactory for lubricating the shaft bearings. Alternately stated, gear pumps have not been satisfactorily used for pumping fluids such as fuels at both high speeds and pressures wherein the fluid comprises a poor bearing lubricant. Instead, when poor lubricating fluids are pumped, the gear pump is operated at a relatively low speed to prolong bearing life, or is replaced in favor of a vane pump or the like capable of high speed operation and having independent bearing lubrication. However, vane-type pumps tend generally to be more expensive and less accurate than gear pumps, and are subject to premature failure due to high wear resulting from the required precise tolerances for satisfactory operation.
The prior art shows substantial effort relating to improvements in gear pump bearings and bearing lubrication. See, for example, U.S. Pat. No. 2,931,303 showing a fixed sleeve or bushing bearing arrangement. Other designs include axially floating, pressure loaded bearings such as those shown and described in U.S. Pat. Nos. 2,472,031; 2,527,941; 2,696,172; 2,870,718; and 3,003,425. Still other bearing designs include relatively expensive roller bearing systems such as those shown in U.S. Pat. Nos. 3,003,426, 3,083,645; and 3,203,355. However, none of the aforementioned bearing systems have been satisfactory for extended use in high speed fuel pumping applications, primarily because of bearing lubrication difficulties. This is particularly true wherein the pumped fuel comprises jet fuel or aviation gasoline, both of which are widely known as poor bearing lubricants.
The high speed pump of this invention overcomes the problems and disadvantages of the prior art by providing a gear pump having meshing pumping gears carried on rotatable shafts received in a bearing arrangement including axially and rotationally floating bushings designed for use under high speed, high pressure pumping conditions with poor lubricant fluids such as jet fuel and aviation gasoline.